This invention relates generally to the field of land vehicles, and more particularly to an occupant-propelled threewheeled scooter or skate-type vehicle. One species of such vehicle has been called "cambering vehicles" by some prior inventors. Vehicles of the three-wheeled scooter type are disclosed in U S. Pat. Nos. 4,165,093, 4,123,079, 4,076,270, 4,088,338, 4,071,261, 4,047,732, and 4,540,192.
A cambering vehicle typically includes a single front wheel mounted at the lower end of a rearwardly inclined pivotable fork controlled by handlebars, and two rear wheels at the ends of struts extending rearward from the steering head. Footpads are provided along the struts. In most cases, the struts may pivot up and down independently, and the rear wheels are mounted upon axles that are fixed with respect to the struts.
In the U.S. Pat. No. 4,540,192 (Shelton), in contrast to the cambering vehicles, the struts cannot move vertically with respect to the fork or vertically with respect to each other; instead, the rear wheels have caster mountings which may pivot in relation to the struts, about respective vertical axes. My vehicle is more like that of Shelton in these respects; however, Shelton's vehicle is also characterized by the fact that its footboards are mounted for independent lateral movement, because it is intended to be propelled by moving the boards alternately together and apart, rather than in unison from side to side. The relative difficulty of riding a device with independent footboards can readily be imagined.
Thus, the prior Vehicles have had to provide footpad struts that were independently swingable, either vertically, in order to obtain the cambering of the front wheel necessary for propulsion, or horizontally. The result of either construction is an inherently unstable structure unsuitable for use by many people.
Shelton's device included rear casters having vertical kingpins, and return springs Were provided to encourage the wheels to return to the straight-ahead position. In this respect, my vehicle represents a significant departure from Shelton and from the other prior devices. I have found that one may obtain easier propulsion, and simpler construction, by providing the rear wheels of a vehicle of this type with caster mountings having pivot axes that are inclined forwardly with respect to the vertical, in the direction of motion. With this arrangement, the casters are biased by the weight of the vehicle and operator, to the forward position; return springs or the like are not required. In addition, the footboards of my vehicle are rigidly interconnected, both laterally and vertically, to provide a stable platform for the operator, whose rhythmic side-to-side motion produces a forward thrust at the casters that propels the vehicle forward.